1. Field of the Invention
The present invention relates to fastener assemblies, and more particularly to an improved nut which automatically locks to a shaft.
2. Description of the Related Art
It has been described by the applicant in the publication WO 93/05307 of Sep. 2, 1992, a nut with positive and automatic locking intended to be screwed on a shaft having a serrated thread, said nut comprising a locking element having serrations on its internal diameter, intended to fix the nut in rotation on the shaft, this locking element being confined in a counterbore of the nut and axially movable in said counterbore between a first locked position and a second unlocked position, characterized in that the locking element is composed of several segments of serrated ring, the different segments being jointed by a resilient circular ring.
This publication describes, in a first embodiment, that the disengagement of the serrations of the locking element from the serrations of the shaft is obtained by a radial motion and that in a second embodiment it can also be obtained by a rotational motion of the segments of the locking element round geometrical axis going through perpendicularly and in its center, the perpendicular section of the resilient ring that allows to embody the different segments.
The object of the present invention relates principally to an improvement of the second embodiment of said publication.
Many types of nuts with positive locking are already known, the most common one is the castellated nut associated with a pin installed in a hole of the shaft on which the nut is screwed and which extends at one and the same time in this hole and in two crenels of the nut.
This particular type of nut has some disadvantages inherent to its structure, particularly an insufficient strength, a poor reaction to the vibrations and a limited effectiveness.
It has been improved by introducing a locking device in the nut with positive locking. This type of nut is particularly described in the documents FR-A-2 358 580 and U.S. Pat. No. 4 328 720.
Document EP-0 102 898 describes a particular example of a nut device with positive automatic locking intended to be fixed in rotation on the shaft and having a locking element.
In this document, the locking element has the shape of threaded ring confined in a counterbore of the nut with which it is associated in rotation. The ring has serrations along its internal thread intended to cooperate with the complementary serrations of the threaded portion of the shaft when both thread threads of the ring and the nut are in phase.
Nevertheless, the effectiveness of such a nut may be compromised under the effects of vibrations.
Document FR-A-2 321 625 describes a lock nut comprising mainly a ring with internal serrations and an opened toric ring lodged in a circular groove located on the external part of this ring. One should note on the one hand that this ring is made in one piece, and on the other hand that this ring is, in this case, acting as a retainer circular clip in said nut to lock.
Document GB-A-547 624 mentions the possibility of a locking obtained by pressure of the threads of the nut on those of the shaft, pressure obtained by a resilient toric opened ring pressing radially a rear and solidary skirt of the nut partially made malleable by radial millings. It will also be noted that the artificial segmentation obtained by millings in the nut is integrally making part of the nut. From another side, the obtained locking is a limited locking and only based on the friction capacities of the thread of the nut in relation to the thread of the screw.
Document U.S. Pat. No.830,787 describes a nut having on its rear part a protrusion, of squared shape, intended to be able to manipulate it with a special closed key provided itself, with an internal cutting of a squared shape of same size that those of the nut. Another particularity of this nut is, that it comprises in the middle of only one flat of its squared shape, a movable pawl on a rotation axle incorporated in the nut. This pawl is stressed by the pressure of a cylindrical compression spring intended to be lodged in the single groove machined on the thread of the screw. The particular wrench is provided in its entry with a special machining intended, during the engagement of this one on such a nut, to provoke the rocking of the pawl on its rotation axle and to allow so to disengage it from the groove in order to be able to move the nut on the screw.
The inconvenient of such a nut are easily noted which, on the one hand, requires a very specific particular tool and on the other hand provides the possibility to lock the nut only every 360.degree. . . . which means at each turn of the nut.
Document U.S. Pat. No. 1,414,761 describes, as regard to it, a nut similar to the previous one which is also provided with only one anti-rotation pawl but which is different from the previous one:
by its external hexagonal shape; PA1 by the necessity to use an adjusting wrench which rocks, during its installation, the anti-rotation pawl; PA1 by the possibility to machine on the screw a wider quantity of grooves in order to increase the number of locked position on the 360.degree. of one turn of a nut.
It may be easily noted that such a nut which is still provided with only one locking pawl and which could not be provided with more, regarding the conception of the recommended installation tool, it is to say an adjusting wrench, the total number of locking positions on one turn of a nut will always and exclusively be restricted to the number of grooves on the screw; moreover, the necessity to be obliged to use always an adjusting wrench restricts the applications of such a nut to the only locations where there is a large radial access to the nut, which is unfortunately not the case of most usual mechanical applications.
Finally, document EP-0 608 246 B1 describes an automatic positive locking nut intended to be screwed onto a shaft having a serrated thread, said nut comprising a locking element having serrations on its internal diameter intended to fix the nut in rotation on the shaft, this locking element being confined in a counterbore of the nut and being axially movable in said counterbore between a first locking position and a second unlocking position characterized in that the locking element is constituted by several segments of serrated ring, the different segment being rendered jointly responsible by a circular resilient ring. Said locking position corresponding to the position for which the serrations of each segment of the locking element cooperate perfectly with the complementary serrations along the thread of the shaft, and said unlocking position corresponding to the position in which the serrations of each segment of the locking element are totally disengaged from the serrations along the thread of the shaft. Said patent mentions, in a first embodiment, that the disengagement of the serrations of the locking element from the serrations along the thread of the shaft is obtained by a radial motion of the segments of the locking element and that in a second embodiment it can also be obtained by a rotational motion of the segments of the locking element round geometrical axis going through perpendicularly and in its center, the perpendicular section of the resilient ring that allows to embody the different segments. Although this second embodiment would work perfectly, it can be noted that in practice the rotational motion of the segments in the space is wide-spreading. Moreover, this rotational motion having to be done in a counterbore machined in the rear part of said nut, the external sizes of the nut have to be adjusted in accordance and so that the result will be an oversized nut comparatively to a commercial standard nut of same thread size, with a more important additional weight prejudice.